Thermoresponsive materials chains

Thermoresponsive polymers containing short oligo(ethy-lene glycol) side chains have been proposed as an attractive alternative to PNIPAAm. PEG is an uncharged, water-soluble, nontoxic polymer used to prepare biocompatible materials, such as biosensors and dmg delivery systems.Lutz ... 

Thermoresponsive control over the display of RGD peptides has been demonstrated by Okano and co-workers (Ebara et al., 2004). A temperature-sensitive copolymer, poly(A-isopropylacrylamide-co-2-carboxyisopropylacrylamide), is grafted on a surface and then decorated with RGD by attachment of the peptide to the carboxylic acid functionalities of the polymer. Cell adhesion is promoted at temperatures above the LCST but reduced below the LCST. This is explained with a modulation of the availability of the peptide at the material surface above the LCST, the polymer is collapsed and the peptide is available at the surface, whereas below the LCST, the polymer becomes soluble and the expanding polymer chains prevent access to the peptide (Figure 3.7(c)). 

Polymer gels with amino acid groups or peptides in their side chains have been synthesized [22,23]. The copol)mier gel between methacryloyl-L-alanine methyl ester (MA-L-AlaOMe) and 2-hydroxypropyl methacrylate (HPMA) shows thermoresponsivity. However, as the HPMA fraction increases, the thermoresponsivity decreased. This gel not only shows thermoresponsivity but also pH responsivity. When the gel is made by irradiating y-rays onto a sequential polypeptide, elastin, also shows thermoresponsivity [24]. These materials consist of biocompatible amino acids and peptides and therefore applications in biorelated areas are possible. 

Zhou et al. developed a novel aqueous thermoresponsive adsorbent material for DNA deposition. A 4-branched chain, starshaped copolymer was developed with each chain comprising a cationic poly(iV,iV-dimethylaminopropyl acrylamide] [PDMAPAAm] block forming the inner domain for DNA binding and a thermoresponsive poly(iV isopropylacrylamide] [PNIPAM] block, the most commonly used thermosensitive polymer, formed the outer domain for surface adsorption [42]. The copolymer and the luciferase-encoding plasmid DNA were complexed and polyplexes of size approximately 100 nm were obtained. The polyplex so formed exhibited LCST at 35°C and was deposited on the substrate by precipitation from an aqueous solution upon warming. Thus, enhancement in the transfection efficiency was observed. 

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